This number (19) is mentioned in Verse 30 of Chapter 74 of the Qur'aan. Apparently, it refers to the number of angels appointed as guards/supervisors over Hell. But the very next Verse in the Qur'aan indicates that this number has a greater significance.
Then in 1974, one Rashad Khalifa discovered that the number is involved in a mathematical code inherent in the Qur'aan. For example, the very first Verse (بسم الله ٠٠٠٠) of the Qur'aan has 19 letters of the Arabic alphabet. The total number of the Chapters in the Qur'aan is 114 which is a multiple of 19, and so on.
It is also indicated that the same number 19 could mislead some people to wrong assumptions. Rashad Khalifa seems to have fallen prey to some such assumption about himself. He went to the extent of saying that two of the Verses in the Qur'aan are interpolations! He seems to have lost sight of Verse 15:9, which informs us unequivocally that Allah will Himself protect the Qur'aan!!
However, it is a fact that the Qur'aan is replete with mathematical codes, not only involving 19 but involving other numbers like 7, 10.
The Code of 19 happens to apply also to the divine phrase يا أيها الناس (O mankind), with which, Allah Himself addresses mankind or asks Prophet Muhammad to address them. One Verse, where Prophet Solomon had addressed his people thus, is excluded. The Verses are: 2:21, 2:168, 4:1, 4:170, 4:174, 7:158, 10:23, 10:57, 10:104, 10:108, 22:1, 22:5, 22:49, 22:73, 31:33, 35:3, 35:5, 35:15, 49:13.
19 is a prime number, indivisible by any other number. By addressing mankind 19 times in the Qur'aan, Allah may be indicating the truth of them all being but one community. The Pandemic Covid-19 has proved that. People living anywhere in the world have all the same needs, and they are all affected by the same problems!
2nd January 2022.